OK, hold the phone.
It's tough to get much simpler than a pair of timer motors and switching contacts. Keep the mechanism greased and it will go forever.
Today's electronics are far more FLEXIBLE than the electromechanical systems, but they certainly aren't any more RELIABLE. The designer is faced with the challenge of interfacing high current, high voltage components (like motors and water valves) to a system that operates outputs at a nominal 5V level and only milliamps to drive. The interface has to withstand the inductive switching currents of coils and solenoids (on the order of several hundred volts for a 12V system). The circuitry must be resistant to water splash, a corrosive environment (typically salt atmosphere), be thermally stable (solder fatigue) when someone runs a hot wash in a 35F degree garage. Then there's the issue of component drift and failure- capacitors have a given life, and cost dictates the lowest workable ratings are typically selected. Then you have the issue of mechanical shock, 3-axis vibe test for the PCB, and all the other physical issues of making a PCB live in a damp, humid, demanding environment.
Not that it can't be done (just look at NASA), but poor board layouts, cheap components, corner cutting on drive ckts, low-cost interconnects and inadequate testing make this a hard sell against a mechanical timer. And then there's the firmware....